Set of thermal afterburners

ABSTRACT

A set of thermal afterburners is described, whose members to a large extent possess the same construction: They have a housing with an inlet for gas to be purified and with an outlet for purified gas. The gas to be purified is freed from impurities with the aid of a burner in a combustion chamber. To conserve energy a heat exchanger is provided, which comprises a plurality of substantially parallel heat exchanger tubes. With the aid of this heat exchanger heat is recovered from the hot gas leaving the combustion chamber and fed to the gas ducted to the combustion chamber. The various members of the set of thermal afterburners now vary in the efficiency level of the heat exchanger, in order to be able to produce a different outlet temperature of the purified gas for each member. For this purpose, the heat exchanger tubes are provided on their surface with elevations and/or recesses, which alter the effective heat exchanger surface area in comparison to smooth-walled tubes. The various members of the set of thermal afterburner now vary substantially exclusively through the density and/or height of the elevations and/or depth of the recesses, but not in the remaining construction, in particular the dimensioning of the various components. In this way, different thermal afterburners can be manufactured at low cost, in the case of which the outlet temperature of the purified gases is adapted to the different needs of the plant connected downstream.

FIELD OF THE INVENTION

The invention relates to a set of thermal afterburners, whose members have in each case:

-   -   a) a housing, which has an inlet for gas to be purified and an         outlet for purified gas;     -   b) a burner arranged within the housing;     -   c) a combustion chamber arranged within the housing, to which         the gas to be purified can be fed and in which the burner         produces a flame;     -   d) heat exchanger comprising a plurality of heat exchanger         tubes, with which heat is recovered from the hot gas leaving the         combustion chamber and to which the gas ducted to the combustion         chamber is fed.

BACKGROUND OF THE INVENTION

Known thermal afterburners, as presently available on the market, possess heat exchanger tubes with a smooth surface. Thus, the efficiency level of the heat exchanger constructed from the heat exchanger tubes is substantially static. The extent, to which heat is recovered from the gases leaving the thermal afterburner and to which heat is fed to the contaminated gases before the combustion chamber, is fixed once and for all. There is however, depending on the plant connected downstream to the thermal afterburner, quite the desire for different discharge temperatures of the purified gas. Up till now for this purpose the heat exchangers of the thermal afterburners used in the individual case were adapted in their capacity by a change in their length. This meant however very profound interference in the fundamental construction of the thermal afterburners, so that sometimes in the case of the various members of this known set of thermal afterburners completely different components had to be used.

SUMMARY OF THE INVENTION

An object of the present invention is to create a set of thermal afterburners whose individual members can be produced more economically.

This object is achieved in accordance with the invention by

-   -   e) providing the outside surface of the heat exchanger tubes         (10) at least in sections with elevations and/or recesses (18);     -   f) the density and/or height of the elevations and/or depth of         the recesses (18) and/or the size of the area of the elevations         and/or recesses for the various members of the set of thermal         afterburners (1) being different, while the remaining         construction of the various members of the set is substantially         identical.

Because in accordance with the invention the heat exchanger tubes are not provided with a smooth outside surface but with elevations and/or recesses on this outside surface, an additional degree of freedom is obtained in setting the desired heat exchanger efficiency level: The more elevations and/or recesses for a given number of heat exchanger tubes and a given diameter of these heat exchanger tubes and the higher and/or deeper they are, the greater the effective heat exchanger surface area and consequently the heat exchanger efficiency level. It is now possible to give the various members of the set of thermal afterburners varying heat exchanger efficiency levels as desired purely by selecting the number and/or height of the elevations and/or depth of the recesses in the case of these various members differently. The length of the heat exchanger tubes and thereby all components associated with this length, thus in particular also the housing, the combustion chamber, the tube bottoms, on which the heat exchanger tubes are fastened at both ends, can remain unchanged. In this way, the individual components of the thermal afterburners can be manufactured economically in greater numbers, with which a substantial price reduction is associated. In some cases, it is also possible to upgrade an already existing thermal afterburner from an existing, no longer desired heat exchanger efficiency level to a new heat exchanger efficiency level by replacing the differently configured heat exchanger tubes.

It is expedient if gas to be purified flows through the heat exchanger tubes and purified gas flows over their outer surface. Then it is therefore possible to occasionally clean off the deposits, which the contaminated gas inevitably leaves behind in the heat exchanger tubes, with a brush, in the same way as a chimney-sweep does. With known thermal afterburners the flow direction was turned around. The clean gas leaving the combustion chamber was ducted through the inside of the heat exchanger tubes, while the gas carrying along the impurities with it impinged the outer surface of the heat exchanger tubes. Here, the purification process was substantially more difficult.

When gas to be purified flows through the heat exchanger tubes, there is the additional advantage that a greater passage area, which is hotter and therefore takes in a higher volume, is available for the purified gas; the throttling is correspondingly reduced.

The housing should possess a removable cover, in particular for gaining access to the heat exchanger tubes in order to clean them.

It is particularly advantageous if the longitudinal axis of the housing runs vertically. With previous thermal afterburners the housing was placed “lying down”, i.e. with a horizontally running longitudinal axis. This was due to the fact that in order to achieve a sufficiently high efficiency level of the heat exchanger comparatively long heat exchanger tubes were necessary, which made the housing very long. Because the room height was insufficient in many cases it was therefore necessary to place the housing “lying down”. Since, however, the housing is exposed to very varying temperatures over its longitudinal direction, special bearings had to be created for the housing, with which in different areas of the housing movement against the support structure connected with the floor was possible, in order to compensate thermal expansion. This was very complex. Due to the greater heat exchanger surface area, which is achieved by the heat exchanger tubes being provided with elevations and/or recesses, these can be kept very much shorter. This again makes it possible to place the thermal afterburner and/or its housing “upright”, even with comparatively small room heights, i.e. to arrange it with a vertical longitudinal axis.

BRIEF DESCRIPTION OF THE DRAWING

An embodiment of the invention is explained in detail below on the basis of the drawing; the single FIGURE shows a vertical axial view through a thermal afterburner in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The thermal afterburner shown overall in the drawing with the reference numeral 1 comprises a housing 2, circular when seen from above, with a laterally arranged inlet flange 3 for exhaust air containing impurities, and an outlet flange 4 for purified air lying diametrically opposite this inlet flange 3, however arranged somewhat higher. The inlet flange 3 communicates with a lower air distribution area 5, which is bounded downwards by a thermally insulated base 6 and upwards on the one hand by the base 8 of a copular isolating and baffle insert 7 and on the other hand by a circular tube bottom 9 surrounding the base 8. The lower ends of a plurality of axis-parallel heat exchanger tubes 10, which all possess the same radial distance from the axis of the housing 2, are fastened in the circular tube bottom 9. The interiors of the heat exchanger tubes 10 at their lower end communicate with the air distribution area 5.

The upper ends of the heat exchanger tubes 10 are fastened in an upper heat exchanger base 11, which extends to an axis-near through-orifice 12 over the entire cross section of the housing 2.

The housing 2 comprises a dome-like cover 2 a, which is tightly but detachably seated on the section 2 b, circular in profile, of the housing 2. Through an upper, axis-near opening 13 of the cover 2 a a burner 14 is led into the inside of the housing 2, which reaches into the orifice 12 of the upper tube bottom 11. The burner 14 is fed with fuel, for example gas through pipes, not shown.

The cover 2 a and the upper tube bottom 11 together bound an upper distribution area 15, which communicates with the upper ends of the interiors of the heat exchanger tubes 10.

Radially inside the isolating and baffle insert 7, open upwards, a cylindrical combustion chamber housing 16, which ends below at a distance from the base 8 of the insert 7 and is open there, extends coaxially.

In contrast to conventional heat exchanger tubes 10 the heat exchanger tubes 10 used here are not provided with a smooth outside surface; instead the heat exchanger tubes 10 within a lower, axial area have a plurality of recesses 18, as a result of which the effective heat exchanger surface area of the heat exchanger tubes 10 is increased in comparison to those with a smooth outside surface. The effective heat exchanger surface area therefore depends not only on the radius and length of the heat exchanger tubes 10 but also on the density distribution of the recesses 18 and on their depth as well as on the length of the axial area, in which recesses 18 are provided.

The circular gap 25 between the housing 2 and the isolating and baffle insert 7 is radially extended by two annular spaces 26, 27. The first annular space 26 is at the lower end of the gap 25 and communicates via a channel 28 with the outlet flange 4. An adjustable butterfly valve 30 lies in the channel 28. The second annular space 27 is approximately below half the height of the gap 25. It is connected via a channel 29, in which an adjustable butterfly valve 31 lies, to the outlet flange 4.

The thermal afterburner 1 illustrated in the drawing works as follows.

The exhaust air to be purified is ducted via the inlet flange 3 into the lower distribution area 5. From there it flows into the lower ends of the heat exchanger tubes 10, passing through these upwards into the upper distribution area 15, from where if necessary swirled by air vanes 19 of the burner 14 enters the combustion chamber 20 arranged inside the combustion chamber housing 16. There, it is heated by means of the burner 14 to a temperature, at which the impurities burn.

The lower end of the combustion chamber housing 16 therefore discharges purified gas, which again flows upwards in the gap between the outer surface of the combustion chamber housing 16 and the inner outside surface of the insulating and baffle insert 7, from there via the upper edge of the insulating and guide set 7, radially outwards, entering the circular gap 25, which lies between the outer surface of the isolating and baffle insert 7 and the inner outside surface of the cylindrical section 2 b of the housing 2 and through which the heat exchanger tubes 10 run. If it is next assumed that the upper butterfly valve 31 is closed and the lower butterfly valve 30 is open, thus the purified gas flows downwards parallel to the heat exchanger tubes 10 and through the lower annular space 26 and the channel 28 reaching the outlet flange 4 and from there to a downstream plant component, e.g. a dryer, where the temperature of the purified gases is used in a suitable way.

The efficiency level of the heat exchanger formed by the heat exchanger tubes 10 obviously depends on the heat exchanger surface area and thus, as already noted above, on the number of heat exchanger tubes 10, on their diameter as well as the number and depth of the recesses 18. Once these parameters have been defined, the efficiency level of the heat exchanger is assured. The exhaust air inflowing via the inlet flanges 3 is therefore heated as it passes through the heat exchanger tubes 10 to a quite specific degree. Accordingly, the temperature of the air leaving the thermal afterburner 1 through the outlet flange 4 likewise drops to a quite specific value.

The burner 14 must feed the exhaust air leaving the heat exchanger tubes 10 with so much energy that their temperature is brought to the heat necessary in the combustion chamber 20 to burn the impurities.

If the thermal afterburner 1 is connected downstream to a plant component for which a different temperature of purified air being fed is required, the efficiency level of the heat exchanger formed by the heat exchanger tubes 10 can be changed accordingly. If, for example, it is required that the temperature of air leaving the outlet flange 4 is higher than in the case of the thermal afterburner 1 shown in the drawing, the efficiency level of the heat exchanger must be reduced. For this purpose, it is sufficient to replace the heat exchanger tubes 10 by such, which present a smaller effective heat exchanger surface area, i.e. particularly by such, which possess a smaller number and/or depth of the recesses 18. All other plant components can remain unchanged with regard to their dimensioning.

In this way, the manufacturer can offer a complete “set” of thermal afterburners 1, which as far as possible can be of identical construction and therefore can be rationally and economically produced, nevertheless being suitable for different application purposes, which require varying outlet temperatures of purified air.

In the case of each member of this set the outlet temperature can be changed by means of the adjustable bypass, which is formed by the upper annular space 27, the channel 29 and the butterfly valve 31. In order to increase the outlet temperature the upper butterfly valve is slightly opened 31 and the lower butterfly valve 30 is closed accordingly. With the aid of the butterfly valves 30, 31 the thermal afterburner 1 to a certain extent can also be adapted to varying flow rates. 

1. Set of thermal afterburners having members comprising: a) a housing, which possesses an inlet for gas to be purified and an outlet for purified gas; b) a burner arranged within the housing; c) a combustion chamber arranged within the housing, to which the gas to be purified can be ducted and in which the burner produces a flame; d) a heat exchanger comprising a plurality of heat exchanger tubes, with which heat can be recovered from the hot gas leaving the combustion chamber and to which the gas ducted to the combustion chamber is fed; wherein e) the outside surfaces of the heat exchanger tubes are provided at least in sections with at least one of elevations and recesses; f) at least one of the density and height of the elevations and depth of the recesses and size of areas, provided with the at least one of the elevations and recesses, for which various members of the set of thermal afterburners are different, while the remaining construction of the various members of the set is substantially identical.
 2. Set of thermal afterburners according to claim 1, wherein gas to be purified flows through the heat exchanger tubes (10) and purified gas flows over their outer surface.
 3. Set of thermal afterburners according to claim 1 wherein the housing possesses a removable cover.
 4. Set of thermal afterburners according to claim 1, wherein a longitudinal axis of the housing runs vertically.
 5. Set of thermal afterburners according to claim 2 wherein the housing possesses a removable cover.
 6. Set of thermal afterburners according to claim 2, wherein a longitudinal axis of the housing runs vertically.
 7. Set of thermal afterburners according to claim 3, wherein a longitudinal axis of the housing runs vertically. 